Jorunna parva and J. pardus

September 10, 2001
From: Nishina Masayoshi

Dear Dr.Rudman,
I've got a email from David W. Behrens(author of Pacific Coast Nudibranchs). He suspects that Jorunna parva looks identical to the Californian species - Jorunna pardus Behrens and Henderson 1981. I was wondering too, as they are very similar to each other.

So I checked Baba's description in Opisthobranchs of Sagami Bay and in Abe's Opisthobranchs of Toyama Bay and other photos. Baba mentioned that radula formula is 12 x 18.0.18 and it has about 11 gills (Opis. of Sagami Bay) to 14 gills (Opis. of Toyama bay). The gills are described as: "gill has a black (Opis. of Sagami bay) or black-purple (Opis. of Toyama Bay) brown line along the branchical veins". If body color is white, those feature are the same.

And your comment "It is possible that these two animals (my animal and Satoru Hori's) are extreme colour forms of the same species" is understandable. Because there are no caryophyllidia on the middle of its back in all J. parva that I can see here.

And length is different, David W. Behrens mentioned "Living animals measure up to 60mm" but I've never heard such a big J. parva. Average length of J. parva is 10mm to 20mm in Japan. So I think those are different animal. Anyhow if we could here from David W. Behrens on the number of gills and caryophyllidia pattern that he's ever seen, it will be helpful for this puzzle.

Here is another puzzle left. In Atsushi Ono's book there is a yellow animal with scattered black
papillae (p.113) which he identifies as J. parva (Baba, 1938). There are caryophyllidia on the middle on its back. He wonders if his J. parva may not be J. parva or an intermediate form
because of the pattern of the caryophyllidia. In Opisthobranchs of Toyama Bay, Abe mentions also that there is a very similar animal which has extreme black caryophyllidia on the middle of its back, but he is not sure whether it is J. parva or not.

Best Regards,
Nishina Masayoshi

nishina@wips.co.jp

Nishina, M., 2001 (Sep 10) Jorunna parva and J. pardus. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5241

Dear Nishina,
Thanks for your thoughts in this and your earlier message. I had also wondered about the Californian species. Both Behrens and Baba mention that the outermost teeth in their species have denticles. As you say though the much larger size that Californian animals grow to may be a problem, unless it is a result of living in colder waters.

Concerning the band down the centre of the mantle. This is not a band where caryophyllidia are absent as in species of Jorunna there is an even cover of caryophyllidia over the whole mantle. What is happening is that some of the caryophyllidia are black while the others are yellow or white - the background colour of the mantle. I mentioned the band in your yellow animal and Satoru Hori's white and brown animal to show they had similarities. It is not necessarily a unique character of the species. If you look at photos of South African specimens of Jorunna sp. 2 both Ernest Seamark's and Valda Fraser's photos show a clear region around the rhinophores and the gills which could be interpreted as the beginnings of the median band. Interestingly one of the South African animals shows the black caryophyllidia scattered individually while in the other they show signs of being clumped in small aggregations.

I suspect Jorunna parva will turn out to be a widespread Indo-West Pacific species with a variable colour pattern.
Bst wishes,
Bill Rudman

Rudman, W.B., 2001 (Sep 10). Comment on Jorunna parva and J. pardus by Nishina Masayoshi. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5241

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